Lemerle Simon, Catalano Manuel G, Bicchi Antonio, Grioli Giorgio
Centro "E. Piaggio" and Dipartimento di Ingegneria dell'Informazione, University of Pisa, Pisa, Italy.
Soft Robotics for Human Cooperation and Rehabilitation, Fondazione Istituto Italiano di Tecnologia, Genoa, Italy.
Front Robot AI. 2021 Mar 12;8:614145. doi: 10.3389/frobt.2021.614145. eCollection 2021.
Living beings modulate the impedance of their joints to interact proficiently, robustly, and safely with the environment. These observations inspired the design of soft articulated robots with the development of Variable Impedance and Variable Stiffness Actuators. However, designing them remains a challenging task due to their mechanical complexity, encumbrance, and weight, but also due to the different specifications that the wide range of applications requires. For instance, as prostheses or parts of humanoid systems, there is currently a need for multi-degree-of-freedom joints that have abilities similar to those of human articulations. Toward this goal, we propose a new compact and configurable design for a two-degree-of-freedom variable stiffness joint that can match the passive behavior of a human wrist and ankle. Using only three motors, this joint can control its equilibrium orientation around two perpendicular axes and its overall stiffness as a one-dimensional parameter, like the co-contraction of human muscles. The kinematic architecture builds upon a state-of-the-art rigid parallel mechanism with the addition of nonlinear elastic elements to allow the control of the stiffness. The mechanical parameters of the proposed system can be optimized to match desired passive compliant behaviors and to fit various applications (e.g., prosthetic wrists or ankles, artificial wrists, etc.). After describing the joint structure, we detail the kinetostatic analysis to derive the compliant behavior as a function of the design parameters and to prove the variable stiffness ability of the system. Besides, we provide sets of design parameters to match the passive compliance of either a human wrist or ankle. Moreover, to show the versatility of the proposed joint architecture and as guidelines for the future designer, we describe the influence of the main design parameters on the system stiffness characteristic and show the potential of the design for more complex applications.
生物调节其关节的阻抗，以便与环境进行高效、稳健且安全的交互。这些观察结果激发了可变阻抗和可变刚度驱动器的发展，从而推动了软关节机器人的设计。然而，由于其机械复杂性、累赘性和重量，以及广泛应用所需的不同规格，设计它们仍然是一项具有挑战性的任务。例如，作为假肢或类人系统的部件，目前需要具有与人关节类似能力的多自由度关节。为了实现这一目标，我们提出了一种用于两自由度可变刚度关节的新型紧凑且可配置的设计，该关节能够匹配人类手腕和脚踝的被动行为。仅使用三个电机，该关节就可以控制其围绕两个垂直轴的平衡方位以及作为一维参数的整体刚度，类似于人类肌肉的共同收缩。运动学架构基于一种先进的刚性并联机构，并添加了非线性弹性元件以实现刚度控制。所提出系统的机械参数可以进行优化，以匹配所需的被动柔顺行为并适用于各种应用（例如，假肢手腕或脚踝、人造手腕等）。在描述了关节结构之后，我们详细介绍了运动静力学分析，以得出作为设计参数函数的柔顺行为，并证明系统的可变刚度能力。此外，我们提供了一组设计参数，以匹配人类手腕或脚踝的被动柔顺性。此外，为了展示所提出关节架构的通用性，并为未来的设计者提供指导，我们描述了主要设计参数对系统刚度特性的影响，并展示了该设计在更复杂应用中的潜力。
